a. Field of the Invention
The present invention relates to a valve means and, more particularly, to a valve means arranged to prevent leakage of fluid such as water, gas, etc. as far as possible and, at the same time, to be operated by an extremely weak force.
B. Description of the Prior Art
Known valve means are arranged, for example, as shown in FIG. 1 and are arranged to open and close a port 3 by moving a valve disk 2 upward and downward by moving a valve stem upward and downward.
The valve means shown in FIG. 1, however, has disadvantages as described below. That is, as the valve is opened and closed by moving the valve stem 1 upward and downward along a lip seal 4, leakage of fluid such as water, gas, etc. occurs at a sliding portion 5 between the lip seal and valve stem. When sealing of said sliding portion 5 is made perfect in order to prevent leakage of fluid, frictional resistance of the sliding portion becomes large and, consequently, it becomes difficult to smoothly move the valve stem upward and downward. Moreover, for said known means, the water pressure applied to the valve disk when closing the valve is large and, therefore, a large force is required to close it.
FIG. 2 shows another example of known valve means for which disadvantages of the valve means shown in FIG. 1 are eliminated to some extent. In this valve means, a cover 12 made of resilient material such as rubber is provided round the valve stem 11 and its end portion 13 is as a valve disk. Besides, said valve means comprises a seal portion 14 which is formed integrally with said cover 12. When the valve stem 11 is pulled upward to open the valve, the valve disk is moved upward by deforming the cover 12 by means of the end portion 11a of the valve stem 11, thus the valve opens. When the valve stem 11 is moved downward, the valve closes. In the valve means shown in FIG. 2, the valve stem 11, cover 13, valve disk 13 and seal portion 14 are formed integrally with each other. Therefore, perfect sealing effect is attained and leakage of fluid can be prevented completely. In case of this valve means, however, the relative movement of the valve stem 11 and cover 12 when opening and closing the valve is large and, moreover, said relative movement is achieved by deformation of the cover 12. Consequently, the cover 12 causes secular change. Therefore, this valve means cannot be used for a long period of time. Furthermore, in case of this valve means, the water pressure in the valve body is also large, and therefore, it is necessary to push the valve stem by a large force when closing the valve.